The influence of the peripheral capacitance vasculature on venous return, right atrial pressure, and ventricular performance has been well documented. While the reflex autonomic influence of myocardial ischemia on the resistance vasculature and the influence of arterial baroreceptor stimulation on the capacitance vasculature have been examined, the reflex effects of myocardial ischemia and infarction on the total capacitance vasculature have not been defined. Such definition is necessary to an integrated understanding of cardiovascular function during myocardial ischemia and infarction. Thus, the applicant proposes to use a canine vena caval to right atrial bypass preparation to assess changes in total intravascular volume during selective coronary occlusion. The influence of the location, duration, and extent of myocardial ischemia and infarction on total intravascular volume will be quantitated. In animals not on bypass, the influence of the reflex on cardiac output will be examined under conditions in which hemodynamic parameters outside of the capacitance vasculature are controlled. The afferent and efferent limbs of th reflex will be delineated with selective surgical ablation and pharmacological blockade in the bypass preparation. In animals in which the splanchnic vasculature is separately perfused and drained, the extent to which splanchnic hemodynamic changes account for the change in total capacity will be examined. Also, the influence of sinoaortic and left atrial baroreceptor stimulation on the reflex volume response will be examined. Finally, a new technique will be developed to assess the reflex influence of coronary occlusion on intravascular volume in the conscious dog. These studies are expected to provide new insights into the control of the capacitance circulation and the interactive influences of the left ventricle and capacitance vasculature during myocardial ischemia and infarction.